Chem Notebook COmplete

%yield = 6.1 tons × 100 = 64%
9.6tons
Discussion
Due to chemical equilibrium or the mass action law, the limiting reagent may not be completely
consumed. Thus, a lower yield is expected in some cases. Losses during the recovery process of the
product will cause an even lower actual yield.
Example 2
A solution containing silver ion, Ag + , has been treated with excess of chloride ions Cl − . When dried,
0.1234 g of AgCl was recovered. Assuming the percentage yield to be 98.7%, how many grams of
silver ions were present in the solution?
Hint:
The reaction and relative masses of reagents and product are:
The calculation,
Ag + (aq) + Cl − (aq) → AgCl(s)
107.868 + 35.453 = 143.321
0.1234 g AgCl ×107.868 g Ag + =0.09287 g Ag +
143.321g AgCl
shows that 0.1234 g dry AgCl comes from 0.09287g Ag + ions. Since the actual yield is only 98.7%,
the actual amount of Ag + ions present is therefore
0.09287 g Ag + = 0.09409 g Ag +
0.987
Discussion
One can also calculate the theoretical yield of AgCl from the percentage yield of 98.7% to be
0.1234 g AgCl =0.1250 g AgCl
0.987
From 0.1250 g AgCl, the amount of Ag + present is also 0.09409 g.
Stoichiometry - A Review
Skills Taught
evaluate molecular weight for a given formula
evaluate weight (mass) percentages of elements for a given formula
evaluate amounts (in mass and mole units) produced in a chemical reaction from given
conditions
classify reactions by types: combination, combustion, displacement, formation, etc
determine the chemical formula when weight percentages are given and then evaluate the
mole percentages of elements in the formula
determine the chemical formula when weight percentages are given and molecular weight is
known
determine the amount produced, the actual yield, and other stoichiometry quantities for a given
reaction